Positioning system, position information transmitter, communication terminal, and control method of the positioning system

ABSTRACT

A position information transmitter including: a digital processing device including a CPU and a position information database storing position information of the position information transmitter and information of channels used by other position information transmitters; and a radio transmitting device executing a signal modulation, wherein the digital processing device generates spread spectrum signals from the position information of the position information transmitter and information of channels used by other position information transmitters, by using the C/A code, and the radio transmitting device modulates the spread spectrum signals and transmits modulated signals as a radio signals.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 12/379,714, filedFeb. 27, 2009. This application relates to and claims priority fromJapanese Patent Application No. 2008-102715, filed on Apr. 10, 2008. Theentirety of the contents and subject matter of all of the above isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a positioning system, a positioninformation transmitter, a communication terminal, and a control methodof the positioning system and, particularly, to a technology thatenables stable and reliable acquisition of the current position of thecommunication terminal.

2. Background Art

A system utilizing radio signals transmitted from artificial satellitessuch as GPS satellites (hereinafter, satellite positioning signals) hasa problem that the positioning accuracy deteriorates or positioningbecomes impossible when a communication terminal such as a GPS receiverenters an area where the satellite positioning signals may not bereceived such as an indoor area, a street with buildings, or anunderground mall.

Therefore, for example, Japanese Patent Application Laid-OpenPublication No. 2007-278756 discloses a technology of providing anapparatus transmitting a position information signal, which is a signalindicative of a position, to an area where the satellite positioningsignals may not be received such as an indoor area or an undergroundmall to allow the communication terminal to receive the positioninformation signal and acquire the current position.

To enable stable and reliable acquisition of the current position of acommunication terminal by a communication terminal capable ofpositioning with the satellite positioning signal and positioning withthe position information signal as in the above technology, anarrangement is required to appropriately determine which of thesatellite positioning signal or the position information signal shouldbe received to set the operation state of the communication terminal.

SUMMARY OF THE INVENTION

The present invention was conceived in view of the above background andit is therefore the object of the present invention to provide apositioning system, a position information transmitter, a communicationterminal, and a control method of the positioning system capable ofstable and reliable acquisition of the current position of thecommunication terminal.

In order to achieve the above object, according to a major aspect of thepresent invention there is provided a positioning system comprising aposition information transmitter including a transmitting part thattransmits a position information signal as a signal compatible with asatellite positioning signal that is a radio signal for positioningtransmitted from an artificial satellite, the position informationsignal being a radio signal containing position information that isinformation indicative of a position; and a communication terminalincluding a positioning processing part that when receiving thesatellite positioning signal, finds a current position of thecommunication terminal by finding a position of the artificial satellitefrom the satellite positioning signal, the positioning processing partupon receipt of the position information signal finding a currentposition of the communication terminal based on the position informationcontained in the position information signal, and a plurality ofcorrelators each capable of independently receiving the radio signals,the transmitting part transmitting the position information signalcontaining operation mode determination information that is informationfor use in determining which of the satellite positioning signal or theposition information signal each of the correlators is to receive, thecommunication terminal including an operation mode setting part thatsets which of the satellite positioning signal or the positioninformation signal each of correlators is to receive based on theoperation mode determination information contained in the receivedposition information signal.

According to the present invention, the current position of acommunication terminal may stably and reliably be acquired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a schematic configuration of a positioning system1;

FIG. 2 is a block diagram of a position information transmitter 100;

FIG. 3 depicts an example of a position information database 1122;

FIG. 4 is an explanatory flowchart of a transmission process of theposition information signal executed by the position informationtransmitter 100;

FIG. 5 is a block diagram of a communication terminal 200;

FIG. 6 is an explanatory flowchart of an operation mode setting process;

FIG. 7 is an exemplary setting of the correlators in the operationmodes;

FIG. 8 is an explanatory flowchart of a positioning process;

FIG. 9 is an explanatory flowchart of the positioning process based onthe satellite positioning signal (S814);

FIG. 10 is an explanatory flowchart of the positioning process based onthe position information signal (S815);

FIG. 11 is an explanatory flowchart of the position determinationprocess (S1017);

FIG. 12 depicts an exemplary setting of the correlators in the operationmodes; and

FIG. 13 is an explanatory flowchart of the operation mode settingprocess.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will now be described withreference to the drawings. FIG. 1 depicts a schematic configuration of apositioning system 1 described as the embodiment of the presentinvention. As shown in FIG. 1, the positioning system 1 includes aplurality of artificial satellites 2 transmitting radio signals forpositioning (hereinafter, satellite positioning signals), a plurality ofposition information transmitters 100 transmitting radio signalsincluding information indicative of positions (hereinafter, positioninformation signals), and communication terminals 200 having a functionof acquiring the own current position based on the radio signals fromthe artificial satellites 2 or the position information transmitters100.

The artificial satellites 2 are, for example, artificial satellites inpositioning systems such as GPS (Global Positioning System), Galileopositioning system, GLONASS (Global Navigation Satellite System), andQuasi-Zenith Satellites. It is assumed that the artificial satellites 2are GPS satellites and that the satellite positioning signals, i.e., GPSsignals transmitted from the artificial satellites 2 are L1 signals(1575.42 MHz) or L2 Signals (1227.6 MHz) in the following description.

The satellite positioning signals sent from the artificial satellites 2include so-called navigation messages. A navigation message includes atotal of 25 frames, for example, and each frame includes five sub-framesand a sub-frame is made up of 300 bits. Each sub-frame includescorrection information of satellite clock, precise orbit information(ephemeris), general orbit information (almanac), ionosphere correctioninformation, UTC correction information, and health information ofartificial satellites, for example.

The satellite positioning signals sent from the artificial satellites 2are subjected to BPSK (Bi Phase Shift Keying) modulation with a C/A code(Coarse/Acquisition code) that is a pseudorandom code (PRN number(Pseudo Random Noise Code)) uniquely added to each of the artificialsatellites 2.

The position information signals transmitted from the positioninformation transmitters 100 are compatible with the satellitepositioning signals transmitted from the artificial satellites 2 and aretransmitted as radio signals having the modulation mode and the frameconfiguration same as the satellite positioning signals. Each of theposition information transmitters 100 is given a C/A code and theposition information signals are subjected to the BPSK modulation with aC/A code of the transmitting position information transmitters 100.

FIG. 2 is a block diagram of the position information transmitter 100.As shown in FIG. 2, the position information transmitter 100 includes adigital processing part 110, a radio transmitting part 120, a clock part130, a sensor part 140, an operating part 151, a displaying part 152, acommunication I/F 153, and a power source part 160.

The digital processing part 110 includes a CPU 111 and a storage part112 (e.g., a storage device, for example, RAM (Random Access Memory),ROM (Read Only Memory), and a non-volatile memory such as flash memory).

The CPU 111 executes programs stored in the storage part 112 toimplement various functions provided by the position informationtransmitter 100. The storage part 112 stores a position informationtransmission program 1121 that is a program implementing a functionabout transmission of the position information signals (hereinafter, aposition information transmitting part) and a position informationdatabase 1122 that has registered data indicative of the position(latitude, longitude, altitude, etc.) where the position informationtransmitter 100 is disposed.

The position information transmitting part implemented by the positioninformation transmission program 1121 generates digital signals (bitstream) through the spread spectrum with the own PRN number (C/A code)from data, such as navigation messages, to be included in the positioninformation signals transmitted from the position informationtransmitter 100 and inputs the generated digital signals to the radiotransmitting part 120.

The radio transmitting part 120 includes a D/A converter 121, a carriergenerating part 122, a modulating part 123, and an antenna 124.

The D/A converter 121 converts the digital signals input from thedigital processing part 110 into analog signals.

The carrier generating part 122 generates a carrier wave of the positioninformation signal based on the clock signal input to the clock part130.

The modulating part 123 modulates (BPSK-modulates) the analog signalinput from the D/A converter 121 with the carrier wave (1575.42 MHz whenthe position information signal is the L1 signal) input from the carriergenerating part 122 and inputs the modulated signal to the antenna 124.

The clock part 130 generates a clock signal for operating the CPU 111and a clock signal (e.g., 1.023 MHz) for generating the carrier wave.The clock part 130 includes an oscillator such as TCXO (temperaturecompensated crystal oscillator) and OCXO (oven-controlled crystaloscillator), for example.

The operating part 151 is a user interface for performing inputoperation to the position information transmitter 100 and includesoperation buttons and switches, for example.

The displaying part 152 is an interface that displays various pieces ofinformation when performing input operation to the position informationtransmitter 100 and when checking the operation state of the positioninformation transmitter 100. The displaying part 152 is a liquid crystalmonitor or LED (Light Emitting Diode), for example.

The communication UF 153 is a communication interface for connecting theposition information transmitter 100 to an external apparatus such as acomputer (information processing apparatus). The communication I/F 153is RS-232C, UART (Universal Asynchronous Receiver Transmitter), opencollector, TTL (Transistor-Transistor Logic), parallel I/F, and USB(Universal Serial Bus), for example. When registering data to ormaintaining the position information database 1122, a computer isconnected to the position information transmitter 100 through thecommunication I/F 153.

The sensor part 140 includes sensors acquiring information (dispositionposition environment information) indicative of the current surroundingenvironment such as an atmospheric pressure sensor and an illuminancesensor. As described later, the information output from the sensor part140 is used for selecting the position information signal if thecommunication terminal 200 receives a plurality of position informationsignals or for correction when acquiring the current position of itsown.

The power source part 160 supplies drive power to the parts of theposition information transmitter 100.

FIG. 3 shows an example of the position information database 1122. Theposition information database 1122 includes registrations of a boundaryflag 311, a height 312, a disposition position of the positioninformation transmitter 100 (latitude 313, longitude 314), sensorinformation 315, an own device channel 316, surrounding device channels317, etc. The information registered in the position informationdatabase 1122 will hereinafter be referred to as position information.

The information registered in the position information database 1122includes the boundary flag 311, which is set to “1: on” or “0: off”. Theboundary flag 311 is information (operation mode setting information)used for setting which of the satellite positioning signal or theposition information signal is received by each of its correlators. Avalue of the boundary flag 311 is set to “1: on” in the positioninformation transmitter 100(1) disposed near a doorway 31 of a building3 of FIG. 3 and the boundary flags 311 are set to “0: off” in theposition information transmitters 100(2) to 100(5) within the building3, for example.

The sensor information 315 is set as real-time detection values detectedby various sensors.

The own device channel 316 is set as information indicative of atransmission channel (corresponding to the C/A code of the own device)of the position information signal transmitted by the positioninformation transmitter 100.

The surrounding device channels 317 are set as information indicative oftransmission channels (corresponding to the C/A codes of other devices)of the position information signals of other position informationtransmitters 100 disposed around the position information transmitter100.

FIG. 4 is an explanatory flowchart of a transmission process of theposition information signal executed by the position informationtransmitter 100. A letter “S” added to the beginning of referencenumerals stands for step.

When transmitting the position information signal, the digitalprocessing part 110 of the position information transmitter 100 acquiresposition information to be included in the position information signalfrom the position information database 1122 (S411). The digitalprocessing part 110 generates a navigation message including theacquired position information (S412) and stores the generated navigationmessage into a sub-frame (S413).

The digital processing part 110 generates digital signals (bit stream)through the spread spectrum with the own C/A code from the navigationmessage stored in the sub-frame (S414) and inputs the generated digitalsignals to the radio transmitting part 120 (S415). The radiotransmitting part 120 modulates the carrier wave depending on the inputdigital signal to transmit the position information signal from theantenna 124 (S416). The position information transmitter 100 repeatedlytransmits the position information signal generated as above atpredetermined timings.

FIG. 5 is a block diagram of the communication terminal 200. As shown inFIG. 5, the communication terminal 200 includes a baseband processingpart 210, a radio receiving part 220, a clock part 230, a sensor part240, an electric field intensity measuring part 241, an operating part251, a displaying part 252, a communication I/F 253, and a power sourcepart 260. The communication terminal 200 is a GPS receiving apparatus ora portable telephone equipped with GPS, for example.

The baseband processing part 210 includes a CPU 211 and a storage part212. The CPU 211 executes programs stored in the storage part 212 toimplement various functions of the communication terminal 200.

The storage part 212 is, for example, RAM (Random Access Memory), ROM(Read Only Memory), and a non-volatile memory such as flash memory. Thestorage part 212 stores an operation mode setting program 2121 that is aprogram implementing a function of setting an operation mode of thecommunication terminal 200 (hereinafter, an operation mode settingpart), a positioning process program 2122 that is a program implementinga function about acquisition of the current position of the own device(positioning) (hereinafter, a positioning processing part), and aposition correction program 2123 that is a program implementing afunction about position correction with sensor information, etc.,(hereinafter, a position correcting part).

The radio receiving part 220 includes a correlating part 221, an A/Dconverting part 222, a demodulating part 223, and an antenna 224.

The demodulating part 223 generates a signal (herein after, a receptionsignal) by demodulating (BPSK-demodulating) the analog signal receivedthrough the antenna 224 with a clock signal input from the clock part230 and input the generated reception signal to the A/D converting part222.

The A/D converting part 222 converts the reception signal input from thedemodulating part 223 into a digital signal.

The correlating part 221 includes a plurality of correlators 2211capable of concurrent operation (capable of tracking a plurality ofchannels corresponding to different C/A codes). The C/A codes to bedemodulated may independently and respectively be set in the correlators2211. Each of the correlators 2211 compares the C/A code included in thedigital signal input from the ND converting part 222 with a replicapattern (C/A code uniquely stored or generated by the communicationterminal 200) and inputs a signal demodulated from the C/A code includedin the digital signal to the baseband processing part 210.

The clock part 230 generates a clock signal for operating the CPU 211and a clock signal (e.g., 1.024 MHz) necessary for the demodulation bythe demodulating part 223. The clock part 130 include an oscillator suchas TCXO (temperature compensated crystal oscillator) and OCXO(oven-controlled crystal oscillator), for example.

The operating part 251 is a user interface for performing inputoperation to the communication terminal 200 and includes operationbuttons, an operation dial, etc.

The displaying part 252 is an interface that displays various pieces ofinformation and is a liquid crystal monitor, an organic EL panel, etc.

The communication I/F 253 is a communication interface for connectingthe position information transmitter 100 to an external apparatus. Thecommunication I/F 253 is RS-232C, UART (Universal Asynchronous ReceiverTransmitter), open collector, TTL (Transistor-Transistor Logic),parallel I/F, USB (Universal Serial Bus), etc.

The sensor part 240 includes sensors acquiring information (currentposition environment information) indicative of the current surroundingenvironment such as an atmospheric pressure sensor and an illuminancesensor. The electric field intensity measuring part 241 is made up of anRSSI circuit, for example, and inputs a signal indicative of theelectric field intensity of received radio signals to the basebandprocessing part 210.

The power source part 260 supplies drive power to the parts of theportable terminal 200.

FIG. 6 is an explanatory flowchart of a process executed by theoperation mode setting part (operation mode setting process). Theprocess shown in FIG. 6 is automatically or manually started, forexample, when the communication terminal 200 is turned on or when a userperforms a predetermined setting operation.

First, the operation mode setting part acquires the operation modecurrently set in the communication terminal 200. The storage part 212 ofthe baseband processing part 210 stores information indicative of theoperation mode currently set in the communication terminal 200 and theoperation mode setting part acquires this information (S611).

The operation mode setting part sets channels (C/A codes demodulated bythe correlators) for the radio signals (satellite positioning signal orposition information signal) captured by the correlators of thecorrelating part 221 and the center frequency depending on the acquiredoperation mode (S612 and S613). The center frequency is 1575.42 MHz inthe case of the L1 signal, for example. The center frequency is notnecessarily matched completely to this frequency and may be set to aslightly mismatched frequency.

FIG. 7 depicts an exemplary setting of the correlators when fivecorrelators exist. As shown in FIG. 7, if the operation mode is set to“indoor/outdoor” (S611: indoor/outdoor), the operation mode setting partsets four correlators (1 to 4) to channels (8ch, 11ch, 15ch, and 20ch)for the satellite positioning signal and one other correlator (5) to achannel (180ch) for the position information signal.

If the operation mode is set to “indoor” (S611: indoor), the operationmode setting part sets only one correlator (1) to a channel (8ch) forthe satellite positioning signal and four other correlators (2 to 5) tochannels (174ch, 175ch, 179ch, and 180ch) for the position informationsignal.

In either operation mode, at least one correlator (the correlator (5) inFIG. 7) is set to a certain channel (180ch) for the position informationsignal. This is for the purpose of enabling the communication terminal200 to automatically set an operation mode when receiving positionrelation information having a boundary flag set to “1” as describedlater.

Although the case of the correlating part 221 including five correlatorsis described as an example, the number of correlators included in thecorrelating part 221 is not limited to five. For example, if thecorrelating part 221 includes 16 correlators, 14 correlators are set tochannels for the satellite positioning signal and two other correlatorsare set to channels for the position information signal if the operationmode is “indoor/outdoor”. If the operation mode is “indoor”, twocorrelators are set to channels for the satellite positioning signal and14 other correlators are set to channels for the position informationsignal.

FIG. 8 is an explanatory flowchart of a process of acquiring the currentposition of the own device (positioning process) executed by thepositioning processing part.

The positioning processing part monitors in real time whether acorrelator receiving the radio signal (satellite positioning signal orposition information signal) exists based on the signal input from theradio receiving part 220 (S811) and if a correlator receiving the radiosignal exists (S811: YES), the positioning processing part acquires anavigation message included in the radio signal received by thecorrelator (S812).

The positioning processing part checks whether the channel set in thecorrelator receiving the radio signal is a channel for the artificialsatellites or a channel for the position information transmitters todetermined whether the received radio signal is the satellitepositioning signal or the position information signal (s813). In thecase of the satellite positioning signal (S813: satellite positioningsignal), the positioning processing part executes a positioning processbased on the satellite positioning signal (S814). On the other hand, ifthe received radio signal is the position information signal (S813;position information signal), the positioning processing part executes apositioning process based on the position information signal (S815).

FIG. 9 is an explanatory flowchart of the positioning process based onthe satellite positioning signal (S814).

As shown in FIG. 9, the positioning processing part determines whether aplurality of satellite positioning signals is received (S911) and if aplurality of satellite positioning signals is received (S911: YES), thepositioning processing part acquires the navigation messages from thesatellite positioning signals (S912). On the other hand, if it isdetermined that a plurality of satellite positioning signals is notreceived (S911: NO), the process is terminated.

The positioning processing part finds positions of the artificialsatellites based on the navigation messages of the satellite positioningsignals acquired at step S912 (S913). The positioning processing partfinds distances (pseudo ranges) from the communication terminal 200 tothe artificial satellites based on the propagation times of electricwaves from the artificial satellites to calculate the coordinates of theartificial satellites from the precise orbit information (ephemeris)included in the navigation messages.

The positioning processing part determines whether the satellitepositioning signals from four or more artificial satellites are received(S914). If the satellite positioning signals from four or moreartificial satellites are received (S914: YES), the positioningprocessing part calculates the current position (latitude, longitude,and altitude) from the positions of the artificial satellites found atS913. On the other hand, if the satellite positioning signals from fouror more artificial satellites are not received (S914: NO), the processis terminated.

FIG. 10 is an explanatory flowchart of the positioning process based onthe position information signal (S815).

As shown in FIG. 10, the positioning processing part determines whetherthe navigation messages acquired at S812 are those transmitted from theposition information transmitter 100 (S1011). If it is determined thatthe navigation messages are those transmitted from the positioninformation transmitter 100 (S1011; YES), the process goes to S1012, andif it is determined that the navigation messages are not thosetransmitted from the position information transmitter 100 (S1011; NO),the process is terminated.

Whether the navigation messages are those transmitted from the positioninformation transmitter 100 is determined by checking whether thenavigation messages (or position information signals) includeinformation indicative of that the navigation messages are thosetransmitted from the position information transmitter 100.

At S1012, the positioning processing part acquires position information(the boundary flag 311, the disposition height 312, the dispositionposition (the latitude 313 and the longitude 314), the sensorinformation 315, etc.) from the navigation messages.

The positioning processing part checks details of the boundary flag 311of the position information (S1013). If the boundary flag is “1; on”(S1013: on), the process goes to S1014. If the boundary flag is “0: off”(S1013: off), the process goes to S1017.

At S1014, the positioning processing part checks the current operationmode set in the communication terminal 200 (S1014). If the currentoperation mode is set to “indoor/outdoor shared mode” (S1014;indoor/outdoor), the positioning processing part sets the operation modeof the communication terminal 200 to the “indoor mode” (S1015). On theother hand, if the current operation mode is set to “indoor mode”(S1014: indoor), the positioning processing part sets the operation modeof the communication terminal 200 to the “indoor/outdoor shared mode”(S1016).

The case of the current operation mode set to “indoor/outdoor sharedmode” at S1014 occurs, for example, when a user of the communicationterminal 200 outside of the building 3 comes closer to the doorway 31 ofthe building 3 and receives the position information signal of theposition information transmitter 100(1) in FIG. 1.

The case of the current operation mode set to “indoor” at S1014 occurs,for example, when the operation mode is set to “indoor mode” at S1016 byreceiving the position information signal from the position informationtransmitter 100(1) that transmits the position information signal withthe boundary flag set to “1: on” at the time of passage through thedoorway 31 because a user of the communication terminal 200 passesthrough the doorway 31 of the building 3 and enters into the building 3and the user subsequently comes closer to the doorway 31 to go out ofthe building 3 again and receives the position information signal of theposition information transmitter 100(1) in FIG. 1.

As above, the operation mode of the communication terminal 200 initiallyset at the time of power-on, etc., is set to a operation mode preferablefor the communication terminal 200 automatically acquiring the owncurrent position when the communication terminal 200 receives theposition information signal with the boundary flag set to “1: on” fromthe position information transmitter 100. Therefore, for example, thesetting may automatically be performed in such a way that a rate ofcorrelators receiving the position information signals is increased ifthe communication terminal 200 exists indoors and a rate of correlatorsreceiving the satellite positioning signals is increased if thecommunication terminal 200 exists outdoors. Performing the appropriatesetting of the operation mode as above reduces a period when thecommunication terminal 200 is unable to identify the own currentposition and the communication terminal 200 may stably and reliablyacquire the own current position.

At S1017 of FIG. 10, the positioning processing part executes the nextposition determination process (S1017). FIG. 11 is an explanatoryflowchart of the position determination process (S1017).

In the position determination process (S1017), first, the positioningprocessing part determines whether a plurality of position informationsignals are received (S1117). The case of the communication terminal 200receiving a plurality of position information signals occurs, forexample, when the terminal is located near the center position of thedisposition positions of a plurality of the position informationtransmitters 100 or when the position information signal from theposition information transmitter 100 disposed in a room currentlycontaining the communication terminal 200 is received along with theposition information signals from the position information transmitters100 disposed in other rooms (position information signals transmittedand arriving through a wall, a floor, and a window).

At S1117, if it is determined that the communication terminal 200receives a plurality of position information signals (S1117: YES), theprocess goes to step S1118. On the other hand, if it is determined thatthe communication terminal 200 does not receive a plurality of positioninformation signals (S1117: NO), the process goes to step S1119.

At S1118, the positioning processing part determines the positioninformation signal that should be selected for finding the own currentposition among the plurality of the received position informationsignals.

For example, the positioning processing part compares respectiveelectric field intensities of the position information signals acquiredfrom the electric field intensity measuring part 241 to select theposition information signal having the highest electric field intensity.

For example, the positioning processing part compares values ofatmospheric pressure, illuminance, etc., acquired from the sensor part240 with values of the sensor information in the position informationincluded in the position information signals to select the positioninformation signal having the highest similarity between the values.

For example, the positioning processing part selects the positioninformation signal having the smallest difference between theatmospheric pressure of the sensor information 315 in the positioninformation and the atmospheric pressure acquired from the own sensorpart 240.

For example, the positioning processing part selects the positioninformation signal having the smallest difference between theilluminance of the sensor information 315 in the position informationand the illuminance acquired from the own sensor part 240.

For example, the positioning processing part determines which positioninformation signal is selected based on a comprehensive correlationvalue obtained by performing predetermined weighting of atmosphericpressure, illuminance, etc.

Since the positioning processing part determines the positioninformation signal to be selected based on the result of comparing therespective values measured by the communication terminal 200 and theposition information transmitter 100, i.e., based on the relativerelationship between both values, the position information signal to beselected may be appropriately determined without being affected byenvironmental changes such as changes in the atmospheric pressure andchanges in the illuminance due to changes in sunshine.

At S1119, the positioning processing part finds the own current positionbased on the received position information signal (the positioninformation signal determined at S1118 if a plurality of positioninformation signals are received). For example, the positioningprocessing part defines the own current position as the dispositionheight 312 and the disposition position (the latitude 313 and thelongitude 314) of the position information.

For example, the positioning processing part defines the own currentposition as values of the disposition height 312 and the dispositionposition (the latitude 313 and the longitude 314) of the positioninformation corrected by the sensor information 315 of the positioninformation and values acquired from the sensor part 240.

Specifically, for example, if a difference exists between bothatmospheric pressures, the disposition height 312 acquired from theposition information is corrected based on a relational expression ofthe atmospheric pressure and the altitude (or a table representative ofthe relationship between the atmospheric pressure and the altitude). Forexample, if a difference exists between both illuminance values, thedisposition position (the latitude 313 and the longitude 314) acquiredfrom the position information is corrected based on a table (orrelational expression) representative of the relationship between theilluminance and the position (the latitude 313 and the longitude 314).

As above, the positioning processing part may compare the sensorinformation 315 acquired from the received position information withvalues acquired from the own sensor part 240 to automatically correctthe disposition height 312 and the disposition position (the latitude313 and the longitude 314) acquired from the position information,automatically acquiring the corrected value as the own current position.Therefore, the communication terminal 200 may acquire accurate values asthe own current position.

If the disposition height of the position information transmitter 100and the height of the communication terminal 200 (height of thecommunication terminal 200 carried by a user) are preliminarily known insuch a case that the communication terminal 200 is a portable telephone,the positioning processing part adds or subtracts the difference to orfrom the disposition height 312 and the disposition position (thelatitude 313 and the longitude 314) acquired from the positioninformation to correct the disposition height 312 of the positioninformation.

Although the case of two operation modes (indoor/outdoor and indoor) isdescribed in FIG. 6, the number of the operation modes is notnecessarily limited to two. For example, as shown in FIG. 12, threeoperation modes (outdoor, indoor/outdoor, and indoor) are available.FIG. 13 depicts a variation of the operation mode setting process ofFIG. 6 and is an explanatory flowchart of the operation mode settingprocess in the case of three operation modes.

At S1311 of FIG. 13, the operation mode setting part acquires theoperation mode currently set in the communication terminal 200. Theoperation mode setting part sets channels for the radio signals(satellite positioning signal or position information signal) capturedby the correlators of the correlating part 221 and the center frequencydepending on the acquired operation mode (S1312, S1313, and S1314).

As shown in FIG. 12, if the operation mode is set to “outdoor” (S1211:outdoor), the operation mode setting part sets four correlators (1 to 4)to channels (8ch, 11ch, 15ch, and 20ch) for the satellite positioningsignal and one other correlator (5) to a channel (180ch) for theposition information signal.

If the operation mode is set to “indoor/outdoor” (S1211:indoor/outdoor), the operation mode setting part sets two correlators (1to 2) to channels (8ch and 11ch) for the satellite positioning signaland three other correlators (3 to 5) to channels (175ch, 179ch, and180ch) for the position information signal.

If the operation mode is set to “indoor” (S1211: indoor), the operationmode setting part sets only one correlator (1) to a channel (8ch) forthe satellite positioning signal and four other correlators (2 to 5) tochannels (174ch, 175ch, 179ch, and 180ch) for the position informationsignal.

As in the case of FIG. 6, in any operation mode, at least one correlator(the correlator (5) in FIG. 12) is set to receive a certain channel(180ch) added to the position information transmitters 100.

Even if three operation modes exist, the number of correlators is notlimited to five, as in the case of FIG. 6. For example, if thecorrelating part 221 includes 16 correlators, 14 correlators are set tochannels for the satellite positioning signal and two other correlatorsare set to channels for the position information signal if the operationmode is “outdoor”. If the operation mode is “indoor/outdoor”, sevencorrelators are set to channels for the satellite positioning signal andnine other correlators are set to channels for the position informationsignal. If the operation mode is “indoor”, two correlators are set tochannels for the satellite positioning signal and 14 other correlatorsare set to channels for the position information signal.

If the communication terminal 200 with the operation mode set to“outdoor” receives the position information signal from the positioninformation transmitter 100 with the boundary flag 311 set to “1” (e.g.,the position information transmitter 100(1) of FIG. 1), thecommunication terminal 200 may automatically switch the own operationmode to “indoor/outdoor” or “indoor”.

If the communication terminal 200 with the operation mode set to“indoor” or “indoor/outdoor” receives the position information signalfrom the position information transmitter 100(1) with the boundary flagset to “1”, the communication terminal 200 may automatically switch theown operation mode from “indoor” or “indoor/outdoor” to “outdoor”.

If the communication terminal 200 with the operation mode set to“indoor/outdoor” receives the position information signal from theposition information transmitters (2 to 5) other than the positioninformation transmitter 100(1) with the boundary flag set to “1”, thecommunication terminal 200 may automatically switch the own operationmode from “indoor/outdoor” to “indoor”.

If the communication terminal 200 with the operation mode set to“indoor” or “indoor/outdoor” becomes unable to receive the positioninformation signal from the position information transmitters (2 to 5)other than the position information transmitter 100(1) with the boundaryflag set to “1” for a predetermined time period or more, thecommunication terminal 200 may automatically switch the own operationmode from “indoor” or “indoor/outdoor” to “outdoor”.

If the communication terminal 200 with the operation mode set to“indoor/outdoor” or “indoor” receives the satellite positioning signalfrom the artificial satellites 2, the communication terminal 200 mayautomatically switch the own operation mode from “indoor” or“indoor/outdoor” to “outdoor” (the setting giving priority to thesatellite positioning signal).

The above description of the embodiment is for the purpose offacilitating the understanding of the present invention and does notlimit the present invention. The present invention may be altered ormodified without departing from the spirit thereof and, of course, thepresent invention includes equivalents thereof.

For example, although the communication terminal 200 allocates differentchannels to the own respective correlators in the above description, aplurality of the own respective correlators may be set to receive theposition information signal of the same channel, and the correlators setto receive the position information signal of the same channel maysearch different frequency ranges in a frequency range to be searched inthe set channel.

Specifically, for example, if a frequency range to be searched in theset channel is frequencies f1 to f3, a first correlator is set to searchthe frequencies f1 to f2 (f1<f2<f3) and a second correlator is set tosearch the frequencies f2 to f3.

Since this causes the searching of the channel to be shared andperformed simultaneously in parallel by a plurality of correlators and afrequency range to be searched by each correlator becomes narrow, thesearch time is reduced. As a result, the time required for thecommunication terminal 200 to acquire the own current position isreduced. The frequency range searched by the first correlator and thefrequency range searched by the second correlator are preferably setsuch that overlapping ranges are reduced as much as possible.

For example, the position information signal including the positioninformation including the setting of channels set for the surroundingdevice channels 317 may be transmitted and the communication terminal200 may automatically set the own correlators so as to receive thechannels set for the surrounding device channels 317 in the positioninformation. This reduces the time required for searching the positioninformation signal transmitted from the position information transmitter100 located on the destination, for example, when the communicationterminal 200 is moved and, as a result, the time required for thecommunication terminal 200 to acquire the own current position isreduced.

Although the sensors are exemplarily illustrated as an atmosphericpressure sensor and an illuminance sensor in the above description, thesensors are not limited to these types. For example, the sensors may bea temperature sensor and a humidity sensor. The type of the radiosignals transmitted from the artificial satellites 2 and the positioninformation transmitters 100 are not limited to electric waves. Forexample, the radio signals may be those utilizing light, infrared light,etc.

1. A position information transmitter comprising: a digital processingdevice including a CPU and a position information database storingposition information of the position information transmitter andinformation of channels used by other position information transmitters;and a radio transmitting device executing a signal modulation, whereinthe digital processing device generates spread spectrum signals from theposition information of the position information transmitter andinformation of channels used by other position information transmitters,by using the C/A code, and the radio transmitting device modulates thespread spectrum signals and transmits modulated signals as a radiosignals.
 2. A position information transmitter according to claim 1,wherein the digital processing device generates the spread spectrumsignals further from a sensor information obtained at a sensor attachedto the position information transmitter.
 3. A position informationtransmitter according to claim 2, wherein the sensor information is atleast one of the atmosphere pressure information or an illuminancevalue.
 4. A position Information transmitter according to claim 1,wherein the digital processing device generates the spread spectrumsignals further from a boundary flag whose value is based on a settinglocation of the position information transmitter.
 5. A positioninformation transmitter according to claim 1, wherein the digitalprocessing device generates the spread spectrum signals further from aboundary flag based on which a communication terminal changes acorrelator to receive radio signals from a plurality of correlators eachof which is used to receive one of the position information from theposition information transmitter or satellite positioning signal from asatellite system.
 6. A position information transmitter according toclaim 1, wherein the position information transmitted from the positioninformation transmitter is compatible with satellite positioning signalstransmitted from a satellite system.
 7. A position Informationtransmitter according to claim 6, wherein the satellite positioningsignals are one of the L1 signals with 1575.42 MHz or L2 signals with1227.6 MHz, and modulated by using BPSK (Bi Phase Shift keying).
 8. Apositioning system comprising: a position information transmittertransmitting a position information; and a communication terminalreceiving the position information from the position informationtransmitter and satellite positioning information from a satellitesystem, wherein the communication terminal has a plurality ofcorrelators each receiving one of the position information or thesatellite positioning information based on an operation mode of eachcorrelator, wherein at least one of the plurality of correlators is setto receive the satellite positioning information, wherein thecommunication terminal receives operation mode information from theposition information transmitter, and selects which of the satellitepositioning information or the position information each of theplurality of the correlators receives based on the operation modeinformation.